Study On Preparation Of WC Cemented Carbides By Thermal Mechanical Alloying

Ultrafine W-C powders with high reactive activity can be fabricated by high energy ball milling, thus WC cemented carbides with fine grain sizes and high properties can be easily obtained through in-situ synthesis during the following heating process. The ball milling process of W-C and its effect on reactive temperature and reactive activation energy are studied by differential thermal analysis (DTA), x-ray diffraction (XRD), scanning electron microscopy (SEM) and property test methods. At the same time, TMA parameters, microstructures, properties and failure mechanisms are also studied.During the high energy ball milling, W and C particles are impacted and fined continuously, then W(C) solid solutions with great crystal lattice distortion are formed and WC nucleate and grow up. The reactive temperature of W-C powders ball milled for 10 hours decreases from 1400℃to 1020℃and the reactive activation energy decreases by 22.7%.W-C-M synthesis mechanisms of the gas protect sintering (GPS) and spark plasma sintering (SPS) are the gradual diffusion between atoms, thus it's difficult to obtain totally synthesized WC cemented carbides.It is shown that the microstructure of WC-Co cemented carbides is short-clubbed with the slenderness ratio of 5:1 and length of 2~3μm. Longer ball milling time and higher synthesis temperature increase the reaction activeness of reactants, thus accelerate transformation of Co3W3C and Co2W4C to WC, which improves the microstructural homogeneity, density, hardness, bend strength and wear property. In contrast to the conventional process, WC cemented carbides fabricated by TMA have higher hardness and bend strength. And the strengthening mechanism can be described as follows: WC cemented carbides have interlaced short-clubbed grain, and in the bend strength test, the microcrack generates at WC/WC grain boundary, and may be blocked by interlaced fine-clubbed grains during extending, which induce the intergranular pulling-out. Due to the pulling-out mechanism, fracture-extend energy is greatly expended, thus bend strength is increased. The wear mechanism is groove wear and spalling of WC grains. These cemented carbides have bright future of application in aiguilles and ceramic tools.